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Full text of "Alaskan glacier studies of the National Geographic Society in the Yakutat Bay, Prince William Sound and lower Copper River regions"

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NUNATAK AND CASCADING GLACIERS                        183
the Nunatak Glacier supplies ice only for the land tongue and for not more than a quarter of the sea tongue.
Below the union of the two arms the united trunk glacier flows on for two miles or so, then splits on the east end of the nunatak into two distributaries, the land tongue and the sea tongue. The nunatak against which the glacier splits is a double-crested gneiss hill about 2 miles long and 1440 feet high at the highest point. It is extended westward by a low spur, or tail, of weaker schist and slate with the fiord on one side and a shallow ice-eroded valley on the other. The eastern end of the nunatak, which is somewhat lower than the centre of the hill, gradually narrows and finally descends beneath the glacier; but a crevassing of the ice in this direction may represent subglacial continuation of this hill eastward. Thus the nunatak and its ice-covered extension protect the land terminus from the thrust of the powerful north arm of the glacier, and tend to confine its supply to the south arm.
The Land Tongue, or Smaller Distributary. Gilbert photographed this tongue from two points, and Gannett mapped it as a distributary of the Nunatak Glacier. But in his description of the glacier Gilbert says * "In the hollow separating this knob (the nunatak) from the south wall lay a mass of ice of uncertain relations. It was seen only from the west, and was supposed to be a tongue or distributary arm of Nunatak Glacier. The fact that it lay several hundred feet higher than the tidal arm has raised doubts as to the correctness of the first impression, and I now suspect that it was only the remnant of a former arm of the glacier, stranded as a motionless and slowly-wasting summit mass. On the map of the Canadian Boundary Commission (1895) it is represented as a distributary of the glacier." Our observations and photographs prove clearly that it is a distributary, branching from the main glacier (PI. LXI, A) at a sufficient elevation to permit of its extension down a valley higher than that of the sea tongue, and its termination at a level above that of the tidal end.
This distributary of Nunatak Glacier has suffered very material change since it was described and photographed by Gilbert in 1899. In 1905 the ice surface was smooth, with a slope of about 5, increasing to 10 at the front, and there was no notable crevassing. On the nunatak side there was a small but well-defined lateral moraine, but on the southern side the lateral moraine was very broad and irregular and rose in places 75 feet above the glacier surface. It varied greatly in breadth, being broadest where large amounts of debris had fallen from the mountain wall, and particularly just where the distributary leaves the main valley. The fact that this fallen debris was not moved on to form a more regular band of lateral moraine testifies to the stagnant condition of this ice tongue. For a considerable distance from the valley wall the glacier was hidden beneath this moraine, which, though only a thin veneer, so irregularly protected the under ice that it had a hummocky topography. Recent extension of the glacier front westward was proved by the presence of this moraine-covered ice out beneath the Cascading Glacier. In 1909 ice still existed beneath this lateral moraine, which projected beyond the glacier front. The ice was protected from melting by the moraine which covers it and by the ice block talus that has fallen upon it from the Cascading Glacier, which is perched on the mountain slope above it.
Between the lateral moraines the ice surface was smooth and uncrevassed and evidently stagnant. The ice was rapidly melting, and numerous short streams coursed over
i Glaciers and Glacktion, Harriman Alaska Expedition, Vol. 8,1004, pp. 01-62.